Light, when emitted from a laser, experiences diffraction—the result of which is called “divergence” or a spreading of the light. FIG. 1 is an illustration of light 100 emitted from a laser 102 (mounted on an integrated circuit chip 104) diverging as it approaches an optical fiber 106. Diffraction causes the laser emitted light 100 to expand in a cone shape 108 which, if the distance the light must travel before reaching, an optical fiber 106, for example, is large enough, the light 100 cannot easily be coupled into the optical fiber 106.
Referring now to FIG. 2, as far back as 1997, people have discussed using fiber optic faceplates to eliminate divergence. FIG. 2 shows an example of a faceplate system 200 used to eliminate divergence. However, to be effective, the faceplate 202 must be very close to the optical device, whether it is a laser 204 or a photodetector 206. However, most typical standard or common commercial packaging that surrounds the optical devices, in order to make electrical connections, prevents the a faceplate 202 from being sufficiently close to an optical element to make them a viable choice.
In addition, as shown in FIG. 3, an optical faceplate 302 cannot handle the combination of multiple beams 304, 306 as would be required if multiple devices, for example lasers 308, 310, are intended to couple to the core 312 of a common optical fiber 314, for example, for purposes of device redundancy or combination of multiple wavelengths into the same fiber. This is because a faceplate only transfers input light to its output in a coherent fashion. Thus, as shown in FIG. 3, for a fixed pitch “P” of fibers 314, with a faceplate 302, some of the lasers 308 can not align with the same fibers 314 as other lasers 310 or, as shown, lasers 308 could miss the fibers 314 entirely.
While lenses can be used to refocus light, lenses are difficult to use if there are many lasers or photodetectors that are close together, due to size limitations. Spacing a lens further away from the devices 402, 404 so that a larger lens 406 can be used, such as shown in FIG. 4, allows diffracted light from the beams 408, 410 emitted by the lasers 402, 404 or directed towards photodetectors (not shown) to interact 412 causing the optical equivalent of electrical “crosstalk” between the signals.
If a lens can be placed close enough to the devices (i.e. closer than would allow crosstalk), then light can be focused. However, using a simple lens system 500, such as shown in FIG. 5 still limits the distance “D” that a fiber 502 can be from a device 504.
As shown in FIG. 6A, if a fiber 602 is close enough to the lens 604 and the lens 604 is close enough to the device 606, the light 608 will enter the core 610 of the fiber 602. If, as shown in FIG. 6B, a fiber 602 is too far away from the lens 604, even light collimated or focused by a lens 604 eventually diffracts, resulting in divergence 612 and hence the same overall difficulty.
Using standard fabrication technologies, slightly more complicated lens arrangements can be made, such as shown in FIG. 7, that can extend the distance somewhat, such as shown in FIG. 7A. However, even then, there is a limit to the distance that the fiber can be from the optical device because, as shown in FIG. 7A, the light still eventually diffracts, resulting in divergence 702 and hence the same overall difficulty. Moreover, more complicated lens arrangements, for example, the one in FIG. 7B that adds a second lens piece 704, requires accurate alignment of the second lens piece 704 relative to the first 706.
FIG. 8A is an example of a common commercially available optical connector 800, such as MPO, MPX, MTP, SMC, MT, MT-RJ, etc. connector. The connector is made up of two connector pieces 802, 804 that interconnect. One of the pieces, called a plug 802, is a male-format piece, because it contains precisely spaced and sized alignment features such as guide plates, posts alignment pins, also called guide pins 806, or other alignment feature(s) that coincide with recesses 808 in the female-format mating piece 804. When the two pieces are brought together, as in FIG. 8B, the guide pins 806 slot into the recesses 808 to ensure and maintain alignment between the two pieces 802, 804.
FIG. 9 shows an alternative arrangement 900 of the common commercially available optical connector 800 of FIGS. 8A and 8B. The difference between the connector of FIG. 9 is that the plug 902 is a female-format piece and the receptacle 904 is the male-format piece that contains the guide pins 906.
Industry today uses one, or at most a small number of, optical devices, for example lasers or photodetectors. As such, all of the optical devices readily fit in between the guide pins/guide pin holes of those connectors. Hence, due to the small number of devices the optical devices can be placed on another surface and the connector plugged directly into that other surface so that the fibers can be brought close to the optical devices. However, where large numbers of devices are used, the approach is not scaleable because with larger numbers of devices, areal the extent of the optical devices gets larger than the spacing of the alignment or guide pins that are used in the connectors for alignment purposes.
When large arrays of optical devices are being used, the requirements of standards-based or common commercially available fiber optic connectors dictate that the fibers will be at least a few millimeters from the optical devices. This is far enough so that that the problems discussed above become extremely problematic. The reason for this distance requirement stems from the typical use, in multi-fiber connectors, of the same type of guide or alignment pins in the connectors. FIG. 10 shows two typical commercially available optical connectors 1000, 1002. The first has a female-format plug 1004, whereas the second has a male-format plug 1006. As can be seen in FIG. 10, the guide pins 1008, 1010 protrude from one end of the connector 1006, 1012 and are inserted into the mating connector piece 1014, 1004 to ensure and maintain alignment. The length of these pins 1008, 1010 typically extends about 2 millimeters or more in length beyond the end 1016, 1018 of a connector piece 1012, 1006 thereby forcing any receptacle plug 1004 attached near the optical devices 1020 to be thick enough to accept these pins 1008 when the receptacle 1004 is a female-format one. The same is true if the plug 1006 is the male-format end of the connector 1002, except in this case, the base 1014 of the connector piece must be thick enough to support the guide or alignment pins 1010.
Typical single or double lens systems made with small lenses (microlenses) whether conventional refractive or diffractive ones cannot handle this distance. For typical semiconductor laser geometries, distances of 0.2 millimeters (or about 10% of the distance desired) can be appropriately handled.
Thus, there is a need for a simple mechanism to transfer light from a device array to a fiber array that is small enough in size to be incorporated into a standards-based or common commercially available connector.